5. FUEL SYSTEM

5-0

5 FUEL SYSTEM

5

5. FUEL SYSTEM

5-1

SERVICE INFORMATION

GENERAL INSTRUCTIONS

• When disassembling the carburetor, be sure to service the vacuum piston and float chamber.• Do not bend or twist control cables. Damaged control cables will not operate smoothly.• When disassembling fuel system parts, note the locations of O-rings. Replace them with new

ones during assembly.• Before float chamber disassembly, loosen the drain screw to drain the residual gasoline into a

clean container.• After the carburetor is removed, plug the intake manifold side with a clean shop towel to prevent

foreign matters from entering.• Remove the vacuum diaphragm before cleaning the carburetor air and fuel passages with

compressed air to avoid damaging the vacuum diaphragm.• When the motorcycle is not used for over one month, drain the residual gasoline from the float

chamber to avoid erratic idling and clogged slow jet due to deteriorated fuel.

SPECIFICATIONS

Item StandardVenturi dia. (mm) 22.1

Identification number VE020BFloat level (mm) 18.5

Main jet #110Slow jet #35

Idle speed 1700±100rpmThrottle grip free play 2_ 6mmPilot screw opening 3±1/2

SPECIAL TOOLFloat level gauge

SERVICE INFORMATION......................5-1 CARBURETOR INSTALLATION........5- 9

TROUBLESHOOTING.............................5-1 PILOT SCREW ADJUSTMENT ...........5-10

CARBURETOR REMOVAL....................5-2 FUEL TANK...........................................5-10

AUTO BYSTARTER ................................5-3 AUTO FUEL VALVE.............................5-11

AIR CUT-OFF VALVE.............................5-5 FUEL UNIT.............................................5-12

VACUUM CHAMBER.............................5-5 AIR CLEANER .......................................5-12

FLOAT CHAMBER..................................5-6

Gasoline is very dangerous. When working with gasoline, keep sparks and flames awayfrom the working area.Gasoline is extremely flammable and is explosive under certain conditions. Be sure towork in a well-ventilated area.

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5. FUEL SYSTEM

5-2

TROUBLESHOOTINGEngine is hard to start Misfiring during acceleration• No spark at plug • Faulty ignition system• Compression too low • Lean mixture• No fuel to carburetor

-Clogged fuel filter Engine idles roughly, stalls or runs poorly-Restricted fuel line • Clogged fuel system-Faulty float valve • Ignition malfunction-Incorrectly adjusted float level • Rich or lean mixture

• Engine flooded with fuel • Contaminated fuel-Clogged air cleaner • Intake air leak-Fuel overflowing • Incorrect idle speed

• Intake air leak • Incorrectly adjusted pilot screw• Contaminated fuel • Clogged idle system or auto bystarter passages• Faulty auto bystarter • Incorrectly adjusted float level• Clogged idle system or auto bystarter passages

Lean mixtureRich mixture • Clogged fuel jets• Faulty auto bystarter • Faulty float valve• Faulty float valve • Float level too low• Float level too high • Clogged fuel system• Clogged air jets • Intake air leak• Dirty air cleaner • Improper vacuum piston operation• Flooded carburetor • Improper throttle operation

Backfiring at deceleration• Improper air cut-off valve operation• Lean mixture in idle system

5. FUEL SYSTEM

5-3

CARBURETOR REMOVALRemove the frame body cover. (!2-3)Disconnect the auto bystarter wire connector.

Loosen the drain screw and drain the fuelfrom the float chamber.Disconnect the fuel tube and vacuum tube atthe carburetor.

Loosen the throttle cable adjusting nut andlock nut, and disconnect the throttle cablefrom the carburetor.Loosen the carburetor intake manifold bandand air cleaner connecting tube band screwsand then remove the carburetor.

AUTO BYSTARTEROPERATION INSPECTIONMeasure the resistance between the autobystarter wire terminals.Resistance: 10W max. (10 minutesminimum after stopping the engine)If the reading is not within the limit, replacethe auto bystarter with a new one.

Auto Bystarter Wire

Adjusting Nut

Fuel Tube

Intake Manifold Band

Air CleanerConnecting TubeBand

Throttle Cable

Vacuum TubeLock Nut

5. FUEL SYSTEM

5-4

Connect a hose to the fuel enriching circuit ofthe carburetor. Connect the auto bystarteryellow wire to the positive (+) terminal of abattery and green wire to the negative (-)terminal. Wait 5 minutes and blow the hosewith mouth or vacuum pump. If the passageis blocked, the auto bystarter is normal.Disconnect the auto bystarter from thebattery. Wait 30 minutes and blow the hosewith mouth or vacuum pump. If air can beblown into the hose, the auto bystarter isnormal.

REMOVALRemove the set plate screws and set plate.Remove the auto bystarter from thecarburetor.

AUTO BYSTARTER INSPECTIONCheck the auto bystarter valve and needle fornicks, wear or damage.If any faulty part is found, replace the autobystarter as a set.

INSTALLATIONInsert the auto bystarter into the carburetorbody until it bottoms.Position the set plate into the groove in theauto bystarter and tighten the screws.

• Be sure to install the auto bystarter andset plate properly.

• Install the set plate with its bottomface facing down.

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Auto BystarterScrews

Bystarter Needle

Bystarter Valve

Auto BystarterScrews

Set Plate

Vacuum Pump

Adopter

Set Plate

5. FUEL SYSTEM

5-5

AIR CUT-OFF VALVEDISASSEMBLYDisconnect the vacuum tube from the air cut-off valve.Remove the two screws to remove the air cut-off valve cover, spring and vacuumdiaphragm.

ASSEMBLYInstall the vacuum diaphragm onto thecarburetor.Install the spring and air cut-off valve coverand then tighten the two screws.

VACUUM CHAMBERDISASSEMBLYRemove the two vacuum chamber coverscrews and the cover.

Remove the spring and vacuum diaphragm/piston.

Spring

ScrewsVacuum Diaphragm

• Be sure to set the vacuum diaphragmlip into the groove on the carburetor.

• When installing the air cut-off valvecover, make sure that the vacuumdiaphragm is properly installed.

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Vacuum Diaphragm/Piston

Air Cut-off valve Cover

Spring

Vacuum Chamber Cover

Air Cut-off valve Cover

5. FUEL SYSTEM

5-6

Push the needle holder in and turn it left toremove the needle holder.Remove the spring and jet needle from thepiston.

INSPECTIONInspect the needle for stepped wear.Inspect the vacuum piston for wear ordamage.Inspect the diaphragm for deterioration andtears.

ASSEMBLYInstall the vacuum piston/diaphragm in thecarburetor body and align the tab on thediaphragm with the groove in the carburetorbody.Install the spring.Install the vacuum chamber cover and tightenit with the two screws.

FLOAT CHAMBERDISASSEMBLYRemove the four float chamber screws andthe float chamber.

Vacuum Chamber Cover

• Be careful not to damage the diaphragm.• Hold the vacuum piston while

tightening the vacuum chamber cover.

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Be careful not to damage the vacuumdiaphragm.

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Vacuum Diaphragm

Float Chamber

Jet Needle

Screws

Vacuum Diaphragm

5. FUEL SYSTEM

5-7

Remove the float pin, float and float valve.

INSPECTIONInspect the float valve and valve seat fordamage or clogging.Inspect the float valve and valve seat contactarea for stepped wear or contamination.

Remove the main jet, needle jet holder, needlejet, slow jet and pilot screw.

Clean the removed fuel jets with detergent oiland blow them open with compressed air.Blow compressed air through all passages ofthe carburetor body.

Pilot Screw

• Be careful not to damage the fuel jetsand pilot screw.

• Before removing, turn the pilot screwin and carefully count the number ofturns until it seats lightly and thenmake a note of this.

• Do not force the pilot screw against itsseat to avoid seat damage.

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Float ValveFloat

Float Pin

Valve Seat

Also remove and clean the vacuumchamber and air cut-off valve.

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Worn or contaminated float valve andvalve seat must be replaced because itwill result in float level too high due toincomplete airtightness.

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Slow Jet Main Jet

Needle Jet HolderNeedle Jet

5. FUEL SYSTEM

5-8

ASSEMBLYInstall the slow jet, needle jet, needle jetholder, main jet and pilot screw.

Standard Opening: 3±1/2turns

Install the float valve, float and float pin. Float Valve

Return the pilot screw to the originalposition as noted during removal.

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Float Pin

Pilot Screw Slow Jet Main Jet

Needle Jet HolderNeedle Jet

5. FUEL SYSTEM

5-9

FLOAT LEVEL INSPECTION

Measure the float level.Float Level: 18.5mm

Float Level Gauge

CARBURETOR INSTALLATIONTighten the drain screw.Install the carburetor onto the intakemanifold, aligning the tab on the carburetorwith the cutout in the intake manifold.Tighten the band screw.Install the air cleaner connecting tube andtighten the band screw.Connect the throttle cable to the throttlewheel on the carburetor.

Connect the fuel tube and vacuum tube to thecarburetor.

Connect the auto bystarter wire connector.Perform the following inspections andadjustments:-Throttle grip free play (!3-3)-Carburetor idle speed (!3-6)

Special

Auto Bystarter WireConnector

Vacuum TubeConnecting Tube Band

Throttle Cable

• Check the operation of the float valveand float before float level inspection.

• Measure the float level by placing thefloat level gauge on the float chamberface parallel with the main jet.

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Float Level Gauge

5. FUEL SYSTEM

5-10

PILOT SCREW ADJUSTMENT

* ADJUSTMENT

A tachometer must be used when adjustingthe engine speed.Turn the pilot screw clockwise until it seatslightly and back it out to the specificationgiven.

Standard Opening: 3 ±1/2turns

* CAUTION

Warm up the engine and adjust the throttlestop screw to obtain the specified idle speed.Idle Speed: 1700±100rpmTurn the pilot screw in or out slowly toobtain the highest engine speed.Slightly accelerate several times to make surethat the idle speed is within the specifiedrange.If the engine misses or runs erratic, repeat theabove steps.

• The pilot screw is factory pre-set andno adjustment is necessary. Duringcarburetor disassembly, note thenumber of turns of the pilot screw anduse as a reference when reinstalling it.

• Place the motorcycle on its main standon level ground for this operation.

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Do not force the pilot screw against itsseat to prevent damage.

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5. FUEL SYSTEM

5-11

FUEL TANKREMOVALRemove the frame body cover. (!2-2, 2-3)Disconnect the fuel unit wire connector.

Disconnect the fuel tube and vacuum tube atthe auto fuel valve.

Remove the four fuel tank mounting bolts andfuel tank.

INSTALLATIONInstall the fuel tank in the reverse order ofremoval.

Fuel Unit Wire Connector

Fuel Tank

Auto Fuel Valve

Vacuum Tube

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5-12

AUTO FUEL VALVE

Disconnect the fuel tube and vacuum tubefrom the carburetor.Connect a vacuum pump to the vacuum tubeand apply vacuum. Check if fuel flows out.• The valve is operating normally if fuel flows

out of the fuel tube when the vacuum isapplied.

• The fuel shall stop flowing out when thevacuum pump is disconnected.If the fuel valve does not operate normally,Check the vacuum diaphragm for poorinstallation or damage and inspect the fueltube for clogging.

FUEL UNIT

REMOVALDisconnect the fuel unit wire connector.Turn the fuel unit retainer counterclockwiseand remove the fuel unit.

INSTALLATIONInspect the fuel unit gasket for damage.Install the fuel unit by aligning the groove inthe fuel unit with the tab on the fuel tank.

No Smoking!＊

Fuel Unit

Retainer

Auto Fuel Valve

First clean the fuel tube.＊

Refer to Section 17 for the fuel unitinspection.

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Do not bend the fuel unit float arm;otherwise, the fuel unit metering valueswill be incorrect.

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5. FUEL SYSTEM

5-13

Install the fuel unit retainer and turn theretainer clockwise to secure it.

Connect the fuel unit wire connector.

AIR CLEANERLoosen the air cleaner connecting tube bandscrew.Disconnect the transmission case breathertube from the air cleaner case.Remove the two bolts and air cleaner case.

The installation sequence is the reverse ofremoval.

Make sure that the arrow on the retaineris aligned with the arrow on the fuel tank.

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Retainer

Arrow

Air Cleaner Case